You'll get a variety of responses on this topic, no doubt based on the analysis=paralysis/wind does all
vs. the efficient use of chops/air/tongue schools...

Fwiw, I'll do what I can to help you. N.B. Nothing can substitute for
working one-on-one with a qualified trumpet performer/teacher IN PERSON!

First: the aperture is the opening between the lips, caused by the air
passing through the lips. You cannot control the aperture as such, but
CAN control the muscles surrounding it (the trumpet players ligature, if you will), as well as
the VOLUME (quantity) and VELOCITY (speed) of your airstream.

Second: You cannot control the aperture by tightening the corners of
your mouth. That's correct: you CANNOT control the aperture by
tightening the corners of your mouth. It's not physically possible.

Muscle groups in the body work in opposition to each other: if you flex
the triceps muscle, the biceps goes slack; if you flex the biceps, the
triceps goes slack.

Perhaps the most crucial muscle to the formation of a good, flexible
embouchure is the ORBICULARIS ORIS muscle, which is a sphincter muscle
(think of a drawstring bag or an old-fashioned camera shutter). Opposed
to the Orb. Oris are the risorius and buccinator muscles (the
corner-tightening muscles used by those who use a smile type embouchure --- Note:
many trumpeters who believe they do not use a smile system are still drawing
away from the mouthpiece and tightening the corners as they ascend.)

If one flexes the corners of the lips, the center of the lips grow weak
and cannot efficiently resist the airstream.

Try it: tighten your corners and use the tip of a finger to push apart
the center of the lips (while you are trying to hold the lips closed by
pressing them against each other). You'll find that it is relatively
easy to do so. The air also finds this very easy, and you have little
control over it with this system.

Now try this: let the corners relax (some of you will find this very
difficult to do, so I'd suggest trying both of these exercises in the
mirror so you're actually seeing what you are doing. Perhaps because of
the fact the left side of the brain controls the right side of the face
and vice versa, we often are doing exactly the opposite of what we
THINK we are doing with our face).

Okay, corners relaxed? Now draw the lips slightly toward the center, pursing
them without pushing out in front of the teeth (no fish faces,
please!<G>).

NOW compress the lips and try to pry them apart with your finger. A
much more difficult task, isn't it?

You'll note that it takes less effort to compress the lips by doing
this (and, in fact, flexibility exercises will become extremely easy
for you once you've mastered this technique).

You'll also note that there is a softer, more flexible area in the
center of the lips, which allows you more control over timbre,
articulation, projection, and flexibility, in short: efficiency.

You'll also find that this becomes even easier if your teeth are
separated (particularly the back molars).

This technique actually relieves symptoms of TMJ in brass players
who've been <mistakenly> Thrusting
the lower jaw forward (which is NEVER a good idea, btw: DROP the
lower jaw, by all means, but NEVER thrust it forward--puts WAY too much
strain on the jaw joint!).

Please try these ideas out, and let me know how they work for you, or
if you need further info.

NOTE: Once the embouchure is working efficiently (greatest amount of
return for the least amount of effort) it becomes possible to access
the use of air to perform with seemingly effortless technique. You'll
note I used the term seemingly.
Of course there is always effort expended to create beauty, but there
needn't be anywhere NEAR the excruciating overwork many players force
upon themselves.

I'll address approaches to wide leaps of pitch in another post, since
there are several different techniques which can be applied to make
this more efficient.